Manual code 75803707A.0708
Page 42 of 64
8 VENTILATION
8.1 FANS WITH 5-SPEED AUTO-TRANSFORMER
If it is expected that it will be necessary to vary the air flow rate during startup or use of the air conditioner, an
auto-transformer may be installed to regulate the fan motor input voltage and thus the fan speed.
The auto-transformer affords the possibility to reduce the fan speed in 3 to 5 steps. Each step corresponds to a
15% reduction in the air flow rate.
5-speed auto-transformers
8.2 FANS WITH 0-10 V MODULATING CONTROL (pCO)
This type of fan affords the possibility to modulate the fan speed and thus the air flow rate by way of a 0 - 10 V
control signal. This signal is generated by the pCO microprocessor control in accordance with one of three different
control strategies:
8.2.1 CONSTANT FLOW RATE CONTROL
This control type is recommended in cases where F7 filters are installed on the supply duct in order to avoid
frequent filter changes. With the aid of a pressure sensor, supplied pre-installed inside the machine and connected to the
fan outlet, the pCO is able to calculate the instantaneous air flow rate and thus control the fan speed accordingly to
ensure a constant air flow rate even in the event of clogged air filters which otherwise would significantly reduce the air
flow.
This control type is configured by Tecnair LV during machine testing. The desired flow rate is entered from the
keypad in the relative User parameter (see User Loop in the microprocessor control manual).
8.2.2 CONTROL WITH CONSTANT PRESSURE IN THE UNDERFLOOR OR SUPPLY DUCT
This is the ideal control type for areas divided into a number of different rooms with air distribution through the
underfloor passages or through supply ducts with motorised dampers controlled by local thermostats. In this case once
the desired temperature is reached in a room, the damper is closed, leading to a rise in the pressure in the underfloor
passages or supply ducts and a consequent undesirable increase in the air flow delivered to the other rooms. The
pressure sensor which is supplied pre-installed, informs the microprocessor control of any increase in pressure due to
the partial or complete closure of one or more dampers. The microprocessor control therefore controls the speed of the
fans in order to adjust the air flow rate and bring the pressure back within the set-point range. This solution is suitable for
machines with chilled water coils. On direct expansion machines, it is only suitable with modulating control of cooling
capacity.
This control type is configured by Tecnair LV during machine testing. The desired pressure value is entered
from the keypad in the relative User parameter (see User Loop in the microprocessor control manual).
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